Expand the terms for both sides of the question, then simplify it.
As Yahoo! mentioned, you can expand the term (a+b)^2 by using the identity (a+b)^2 = a^2 + 2ab + b^2.
If you don't know where this identity comes from, you can simply perform multiplication for the term, i.e. (a+b)^2 = (a+b)(a+b), now expand it.
What have you got for now?

"Expand the terms for both sides of the question, then simplify it.
As Yahoo! mentioned, you can expand the term (a+b)^2 by using the identity (a+b)^2 = a^2 + 2ab + b^2.
If you don't know where this identity comes from, you can simply perform multiplication for the term, i.e. (a+b)^2 = (a+b)(a+b), now expand it."